Uniform Resource Locator (URL) is commonly used by a web browser to reference a document at a remote web server. To retrieve the document, a user can either enter the document's URL into an address field of the web browser or mouse-click the URL if it is embedded in another web page. Alternatively, the user can also retrieve the document by entering the URL as a query term into the search box of a search engine. These approaches all work as long as the URL is spelled correctly and the corresponding document is available at the location specified by the URL.
On the other hand, people often encounter inoperative URLs on the Internet. There are many possible causes behind an inoperative URL. It may happen if a user enters a misspelled URL into the address field of the web browser. It also occurs if the misspelled URL is embedded in a web page and the user selects (e.g., mouse-clicks) the URL. Sometimes, an inoperative URL occurs if the document referenced by the URL no longer exists at the URL-specified location (e.g., the document has been moved to a different location) or the web server hosting the document is temporarily or permanently shut down.
Conventionally, after determining that a user-identified URL is inoperative, the web browser displays either a generic error message web page or an error message web page customized by the web server receiving the URL. These error message web pages offer little help if the user does not know how to correct a misspelled URL or if the document referenced by the URL has been relocated. Furthermore, submitting the inoperative URL to a search engine rarely returns useful suggestions, perhaps because the inoperative URL is processed as a regular single-word query term.
In view of the aforementioned, it would be desirable to have a web browser capable of serving relevant information to a user when it encounters an inoperative document link. Further, it would be desirable for a web server to have similar functionalities when receiving an inoperative document link. Finally, when a cached copy of the document referenced by the inoperative document link exists, it would be desirable for a client device to receive, or be offered the opportunity to receive, the cached copy of the document.